True, If you know that the last name never changed, then yes make them both the same, but if it did change having both names better defines the search, (If the name did not change for an Anglo-Saxon, modern woman in the US and Canada because of "lib" preferance, it should be so mentioned in the overview) But if you are unsure, then leave it blank, otherwise you are making the statement that her maiden name and her married name are "in fact" the same which may or may not be true.
I have also noticed that there seems to be a general practice of using the maiden name spot for an alt spelling of the last name (both for men and women) ie James Brown (Browne) (Browne beinng the maiden/alt name). I Mayself have used the maiden name spot when I knew that they changed there name (a very common pratice, and you are asked what you want your american name to be on the aplication for US Citizenship) So a name my end up John/Johann with the last name of James (Schwartz), His american name was John James but his name before he moved to the US was Johann Schwartz. This may confuse an onlooker but when it was within the last few generations the number of people that even notice it are few so there's little explaining to do.
Before you ask how to give a man a maiden name(for those who haven't done it yet). Change him to a female, give him a maiden name, change him back to a male.